1. Field of the Invention
This invention relates to the field of biological indicators and sensors for detecting certain harmful chemical and/or biological agents. More particularly, it pertains to the use of a chemical and/or morphological change in the material of the sensor when a target pathogen or vapor interacts with the sensor. The sensor is inexpensive, sensitive, selective, robust, and covertly deployable.
PCT International Publication No. WO 02/29378 A2 (published on Apr. 11, 2002) is entitled “Sensor for Chemical and Biological Materials,” the contents of which are hereby expressly incorporated herein in their entirety by this reference.
2. Description of the Related Art
The need for detection of chemical and/or biological agents in a variety of applications is acute. In attempts to satisfy this need, the development of biosensors has been a particularly active field in recent years, resulting in numerous concepts and devices. A substantial amount of prior art has been generated by various researchers working in this field and a number of methods have been developed which allow such detection. The most important results of such prior art are discussed below. However, none of the methods described in the prior art is quite acceptable, as subsequently discussed. See, for instance:    (1) B. C. Dave, B. Dunn, J. S. Valentine, and J. T. Zink, Anal. Chem. 1994, 1120A–1127A.
The approaches developed in the prior art typically use encapsulation of enzymes, antigens and/or antibodies in sol-gel matrices as a means of stabilizing their biochemical activity and providing a means to react with smaller molecules that diffuse through the pores of the gel.
Such techniques have typically been applied to immunoassay techniques, but characteristically involve aqueous based chemistry with electrochemical and/or optical methods of detection. These techniques are usually not real-time.
Other approaches to airborne sensing of biomaterials are also available, including mass spectrometry and infrared spectroscopy, but these methods are complex, costly and not readily amenable to covert or continuous, unattended monitoring.
The concept of immobilizing indicator biomolecules onto conductive polymer substrates, i.e., by encapsulation, as well as the development of chemical and biological sensor devices that are based on electroconductive polymers in general, is an area that has attracted considerable recent attention. See, for instance:    (2) A. Guiseppi-Elie, U.S. Pat. No. 5,766,934;    (3) M. Umana and J. Waller, Anal. Chem. 1986, 58, 2979–2983;    (4) N. C. Foulds and C. R. J. Lowe, Chem. Soc., Faraday Trans. 1, 1986, 82, 1259–1264;    (5) C. Iwakura, Y. Kajiya and H. Yoneyama, J. Chem. Soc., Chem. Commun. 1988, 15, 1019;    (6) T. Matsue, et. al. J. Electroanal. Chem. Interfacial Electrochem., 1991, 300, 111–117;    (7) M. Malmors, U.S. Pat. Nos. 4,334,880 and 4,444,892;    (8) M. K. Malmors, J. Gulbinski, III, and W. B. Gibbs, Jr. Biosensors, 1987/88, 3, 71.
However, all of the electroactive biosensors described in the above-mentioned publications are designed to operate in aqueous environments, not in air. The present invention, as subsequently discussed, not only allows for the detection of the chemical and/or biological agents in aqueous environments, but it also has the further advantage of detecting these agents in gaseous environments, such as air, as well.
The present invention applies the concept of using indicator biological materials (hereinafter, biomaterials or biomolecules) for such detection as these biomaterials are first ensconced on electroconductive polymer carriers.
In general, these devices are formed from thin films of electroconductive polymer fabricated on a pattern of microsensor electrodes, which are, in turn, formed on an insulating substrate. Sensor devices that exploit the transducer-active responses of electroactive polymers may be conductometric, as discussed, for example, in:    (9) A. J. Lawrence and G. R. Moores, Eur. J. Biochem. 1972, 24, 538–546;    (10) D. C. Cullen, R. S. Sethi and C. R. Lowe, Anal. Chim. Acta 1990, 231, 33–40.
A number of ways to cause the transducer-active conductometric response has been described. The prior art teaches the use of the large change in electrical impedance for that purpose. See, for example:    (11) A. Guiseppi-Elie and A. M. Wilson, Proceedings 64th Colloid. and Surf Sci. Symp., Jun. 18–20, 1990, Lehigh University, Lehigh, Pa.;    (12) T. Matsue, et. al., J. Chem. Soc., Chem. Commun. 1991, 1029–1031;    (13) M. Nishizawa, T. Matsue and I. Uchida, Anal. Chem. 1992, 64, 2642, 2644;    (14) D. T. Hoa, et. al., Anal. Chem. 1992, 64, 2645–2646;    (15) Guiseppi-Elie, A. U.S. Pat. No. 5,312,762;
A conductometric response that accompanies oxidation and/or reduction of the polymer, the amperometric response, has also been described. See, for example:    (16) L. Gorton, et. al., Anal. Chim. Acta 1991, 249, 43–54.
The use of redox mediation and/or electrocatalysis to cause the transducer-active conductometric response has been also described. See, for example:    (17) M. Gholamian, et. al., Langmuir, 1987, 3, 741;    (18) Y. Kajiya, et. al., Anal. Chem. 1991, 63, 49;    (19) Z. Sun and H. Tachikawa, Anal. Chem. 1992, 64, 1112–1117.
In particular, the potentiometric method, when the electrode potential change that accompanies changes in polymer redox composition is measured, was used. See, for example:    (20) S. Dong, Z. Sun, and Z. Lu, J. Chem. Soc., Chem. Commun. 1988, 993;    (21) S. Dong, Z. Sun, and Z. Lu, Analyst, 1988, 113, 1525;    (22) Z. Lu, Z. Sun and S. Dong, Electroanalysis, 1989, 1, 271;    (23) A. E. Karagozler, et. al., Anal. Chim. Acta, 1991, 248, 163–172;    (24) Y. L. Ma, et. al., Anal. Chim. Acta 1994 254 163–172.
As will be shown below, the detection of the chemical and/or biological agents in accordance with one aspect of the present invention measures transducer-active conductometric response as a result of a morphological as well as chemical change in a polymer film.
A morphological change results when the target chemical or biological agent is absorbed into and retained within the gel as a result of its interaction with the bioindicator. The gel must swell (being somewhat flexible due to its hydrated state) to accommodate this absorbed material, causing the embedded conductive polymer molecules to separate relative to each other, causing a decrease in overall conductivity.
None of the prior art mentioned above teaches or discloses the measurement of the conductometric response as a result of a morphological change.
Furthermore, conductive polymer based sensors have been developed for detecting volatile organic compounds in air, along with chemical weapon simulants. See, for example:    (25) F. G. Yamagishi, et al., Proc. of the SPE Annual Technical Conference and Exhibits, ANTEC 98, XLIV, 1335 (1998).
Other sensor technologies include surface acoustic wave devices (which require complex frequency counting electronics), mass spectroscopy, infrared spectroscopy, and gas chromatography, or some combination or combinations of these methods. These techniques are currently being developed but are primarily directed toward laboratory analysis rather than field application. All of the existing methods of analysis and detection of biological pathogens and chemical agents have serious disadvantages of having large size, long analysis times, complicated electronics support, lack of specificity and/or high cost.
In view of the foregoing, there is a need for a simple, inexpensive and accurate sensor for detection of biological pathogens and chemical agents. A sensor is needed which is also low power, compact, rugged, highly selective, and adaptable to field application for detection of vapor phase pathogens in real time without the need for involving “wet” chemistry. There is no known prior art which teaches a sensor satisfying all these requirements.
A principle that biological materials can be detected by detecting changes in indicator materials due to their interaction through highly specific processes is frequently exploited as a means of determining their presence in various media, under airborne or aqueous scenarios. This invention utilizes this principle and provides for a rugged, low-cost, highly sensitive and selective sensing device suitable for remote real-time covert field monitoring and detecting of relevant biomaterials.
Previously, a biosensor was demonstrated based on the conjugate glucose oxidase/glucose, where the enzyme was encapsulated in a sol-gel matrix, which was in turn coupled with a conductive polymer. This biosensor is described in U.S. Pat. No. 6,730,212, filed on Oct. 3, 2000. In principle, the approach described in U.S. Pat. No. 6,730,212 is applicable to numerous types of bioindicator molecules.
This approach provides for high specificity as well as enhanced stability of the enzyme, since it is physically confined (preventing denaturing) and the aqueous environment and pH necessary for vitality are also included in the pore. The present invention will enhance and enable this concept to meet specific sensing applications.
Such enhancement and fine tuning of the invention described in U.S. Pat. No. 6,730,212 is necessary because it was observed that such encapsulated bioindicators are very sensitive to the chemical and physical properties of certain co-encapsulated conductive polymers such as, for instance, polyaniline sulfonic acid. The technique of this invention provides a means by which this problem may be minimized or avoided.
In particular, the sensor described in U.S. Pat. No. 6,730,212 turned out to be insufficient when the encapsulated bioindicator is a very important enzyme acetylcholinesterase (AChE), described subsequently in detail.
The present invention provides a sensor by combining conductive polymer transducers and encapsulated sol-gel techniques and makes this approach usable even for highly labile enzymes. The combination of these approaches is not found in any other sensor device for the detection of biological or chemical materials.